Future generation semiconductor devices will require thin gate dielectric films having a high dielectric constant and thin metallic films, both films having high purity. Such films are commonly formed using a variety of well documented techniques. However, conventional techniques used to form thin films have typically introduced impurity elements that lower the dielectric constant of the film and degrade the electrical properties of the film material.
In U.S. Patent Application No. 2004008827 entitled “Atomic Layer Deposition of High K Dielectric Films” by Lee et al., a method is discussed to provide a dielectric film by using two portions. A first portion contains silicon dioxide that is pretreated in order to obtain a thin layer. Silicon dioxide has a relatively low dielectric constant of about 3.9. Therefore a portion of the silicon dioxide is removed by a reactive gas in order to obtain a higher dielectric constant for the dielectric stack (the silicon dioxide and the subsequent metal oxide). Various known etchants, including fluorine and chlorine based chemistries, are disclosed to accomplish this removal of silicon dioxide. A second portion of the dielectric film is subsequently formed by atomic layer deposition (ALD) on top of the thin portion of silicon dioxide. However, regardless of which of the disclosed metal oxides is used, the second portion of the dielectric film contains contaminants such as at least one of carbon, nitrogen and silicon. Depending upon which contaminant is present, each of the contaminants functions to significantly degrade various electrical characteristics of the film or to lower the dielectric constant of the film. For example, if silicon is present in the metal oxide, the dielectric constant of the film is lowered. If carbon is present in the metal oxide, the current or gate leakage is increased and the reliability is degraded.
In an article by Gordon et al., entitled “Alternating Layer Chemical Vapor Deposition (ALD) of Metal Silicates and Oxides for Gate Insulators” in the Mat. Res. Soc. Symp. Proc. Vol. 670 of the 2001 Materials Research Society, there is disclosed a method for forming a “pure” metal oxide as an alternative to forming a metal silicate that uses both a silicon precursor and a metal precursor. The metal oxide is described as being formed by using only a metal precursor. However, the metal precursor described therein has both nitrogen and carbon. The ramification of using such a precursor is that the carbon and nitrogen from the precursor are incorporated in the “pure” metal oxide film as impurities. These impurities degrade the electrical characteristics of the resulting metal oxide film.
In an article by Lo Nigro et al. entitled “Fabrication of LaAlO3/Pt(100)/Hastelloy C276 and CeO2(100)/Pt(100)/Hastelloy C276 Multilayers by Metallorganic Chemical Vapor Deposition”, Journal of the Electrochemical Society, 148 (8) F159–F163 (2001), there is described a method of forming a semiconductor thin film. The film is formed by a precursor that contains fluorine for the purpose of delivering the precursor into a reaction chamber. The fluorination of the precursor assists in delivery of the precursor. However, metal oxide made by this method contains precursor impurities including fluorine and carbon. Because fluorine is present in the precursor as part of the ligand of the precursor, an undesired amount of the fluorine is deposited in the thin film.
Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of the embodiments of the present invention.